The present invention generally relates to an electromagnetic rotary drive and more particularly to an electromagnetic rotary drive being designed as a bearingless motor.
The so-called bearingless motor is an electromagnetic rotary drive in which the rotor is journalled without contact with respect to the stator by means of magnetic forces, with no separate magnetic bearings being present for the rotor. In the active motor part, not only a torque but also a magnetic journalling force are produced. For this the stator is designed as a bearing and drive stator which comprises a drive winding for producing a drive field and a control winding for producing a control field. A magnetic rotary field can be produced with the drive and control winding which on the one hand exerts a torque on the rotor which causes its rotation and which on the other hand exerts a transverse force on the rotor which can be set as desired, so that its radial position can be actively controlled or regulated respectively.
In one embodiment of the present invention, an electromagnetic rotary drive which is designed as a bearingless motor in which both the drive field and the control field can be produced in the form of a magnetic rotary field and which is simpler, in particular in regard to its construction, than the known embodiments is proposed.
In accordance with an embodiment of the present invention, an electromagnetic rotary drive, designed as a bearingless motor, is proposed which comprises a magnetically journalled rotor and a stator which comprises a drive winding for producing a magnetic rotary drive field which produces a torque on the rotor, and a control winding for producing a magnetic rotary control field by means of which the position of the rotor with respect to the stator can be regulated, with the stator having exactly six stator teeth.
A rotary drive which is designed in accordance with the principle of the bearingless motor in which both the drive field and the control field can be generated in the form of rotary fields can be realized with only six stator teeth. The prior art had been that the minimum number of stator teeth for a bearingless motor of this kind amounts to eight. The reason for this is as follows: In accordance with the principle of the bearingless motor the numbers of pole pairs of the drive winding and of the control winding must differ by one, which means that in the minimum case one of the windings is bipolar and the other winding is quadrupolar. In order that a rotary field can be produced with each winding, each winding must be designed to be at least two-phased. In accordance with the known prior art the minimum number of stator teeth results from the product of the doubled number of pole pairs and the number of phases, and is consequently equal to eight.
Through embodiments of the present invention it is now proposed to realize a rotary drive of this kind with only six stator teeth. This brings about a considerable simplification of the entire rotary drive. Thus, for example, the construction of the stator and of the rotor respectively and the construction of the windings or of the coils with which the windings are realized respectively is simplified.
In accordance with a first exemplary embodiment, the drive winding and the control winding are designed as separate, which means physically different, windings. The drive winding and the control winding comprise in each case six concentrated coils, with one coil of the drive winding and one coil of the control winding being wound around each stator tooth. In this exemplary embodiment the drive winding and the control winding are in each case designed to be three-phased, which has the advantage that they can in each case be operated with a conventional rotary current controller.
In a second exemplary embodiment, the drive winding and the control winding are realized with the same coils. In this exactly one coil is provided on each stator tooth. Each coil can be controlled separately and independently of the other coils. These six coils thus function both as drive winding and as control winding. The currents which are required for the production of the rotary control field and of the rotary drive field are calculated for each coil, then computationally superimposed and fed in into the corresponding coil.
In the following the invention will be explained in more detail with reference to exemplary embodiments and with reference to the drawings.